Computer technology has advanced to the point where a dental prosthesis may be milled from a solid block of material based on three-dimensional digital data corresponding to a proposed shape of the dental prosthesis. All methods of production begin with a model of the patient's dentition. The dentist will first make an impression of a patient's existing dentition, including the teeth immediately above and to the side of the tooth structure to which the dental prosthesis is to be attached. After first cutting away any unwanted tooth structure, thereby preparing the tooth to which the prosthesis is to be attached, the dentist has the patient bite into an impression material forming a negative impression of the patient's dentition. The negative impression is then filled with dental die stone to make a model. This model should duplicate the occlusion surfaces between upper and lower aligned teeth and the configuration of the prepared tooth structure to which the dental prosthesis is to be attached. Currently there is a newer, less common method of creating a model of the patient's dentition utilizing a digital impression. With digital devices placed in the mouth and using cad/cam technology to produce the finished model, the need for a physical impression is no longer there. Two such systems currently in use in the United States would be the Itero System, manufactured by Cadent and the C.O.S. System from 3M Corporation.
The computer aided design equipment used to make a dental prosthesis has a scanner that is used to scan the surfaces of the model. Scanning may be accomplished either with optical techniques using laser or non-laser light or tactile techniques where a probe physically contacts the prosthesis's surface. The computer aided design equipment converts the model's surfaces into three-dimensional digital data corresponding to the physical shape of the model. This original data collected during scanning is then used to create an image of the proposed shape for the prosthesis on a screen of a computer monitor. The original image displayed on the monitor screen needs to be adjusted to modify the original image to correspond to the ultimate shape of the dental prosthesis. The computer aided design equipment is programmed to allow the technician, with the aid of a mouse and employing conventional point and click techniques, to change the shape of the image.
Because the data originally collected during scanning isn't precise enough to make the dental prosthesis directly based on this data, the technician can and does make adjustments to the data originally provided by the scanner so that the dental prosthesis, at least in theory, fits properly into the patient's mouth. After making such adjustments to the data collected by the scanner, the adjusted three-dimensional digital data is then forwarded to an automatic milling machine that then mills away the unwanted material from a work piece to form the dental prosthesis. Typically, the work piece is a block of material comprised of ceramic, titanium, or a composite plastic material. Conventional investment casting is also used to make a dental prosthesis and a wax pattern may be milled from a work piece of wax that is then used in the investment casting process.